Pyrolytic carbon having the characteristics described in U.S. Pat. No. 3,677,795, issued July 18, 1972 to Jack C. Bokros, is particularly suitable for use in prosthetic devices which are implanted in humans and other living animals because it is thromboresistant, having no adverse reaction with blood, and is biocompatable with body tissues so that it does not induce rejection of the implanted device. While in many applications a prosthesis is formed of a suitable substrate material and thereafter coated with pyrolytic carbon, for certain applications, such as to achieve a desired thinness, it may be desirable to form the entire prosthesis or an entire prosthesis member of pyrolytic carbon.
Articles may be formed from a massive deposit of pyrolytic carbon that is created as described in U.S. Pat. No. 3,399,969 issued Sept. 3, 1968, to Jack C. Bokros et al. Exemplary of prosthetic members which may advantageously be formed entirely of pyrolytic carbon are valve members or occluders for heart valves. Pyrolytic carbon provides the thromboresistance and biocompatibility required of heart valve members which are in continuous contact with blood in a critical organ of the body, and pyrolytic carbon has the wear-resistance necessary for continuously moving heart valves which are permanently implanted in the heart. By forming valve members of strong pyrolytic carbon, the valve members may be made very thin yet have the requisite structural strength.
While the importance of manufacturing heart valves to be as mechanically trouble-free as possible cannot be overstated, any mechanical device may not operate forever in its intended fashion, either because of some mechanical difficulty in the heart valve or as a result of changing conditions within the body. From time-to-time, therefore, it may be desirable to monitor an implanted artificial heart valve so as to assure its continuing functioning in the intended manner. Because implantation in the heart precludes direct examination of a heart valve, it would be desirable that the functioning of the valve may be monitored by X-rays.
Because pyrolytic carbon is sufficiently transparent to X-rays so as not to be detectable when implanted in a human body, it would be desirable to include radio-opaque markers in pyrolytic carbon prosthetic members which do not affect their biocompatability when implanted in a human body.
It is an object of the present invention to provide methods of implanting a foreign body in a substantially integral pyrolytic carbon prosthetic member so that the foreign body is fully encased in the member and so that the member has an uninterrupted pyrolytic carbon surface. More specifically, it is an object of the invention to provide a method of forming a prosthetic member of pyrolytic carbon with a radiographic marker fully encased therein.